Unfortunately the Medium+ density and 0x436 devices have their F_SIZE register
at a different location: 0x1FF800CC instead of 0x1FF8004C. Fix this for
the 0x427 Medium+ devices and also the 0x436 devices. Furthermore, for
0x436 devices the flash size is reported as a 0 or 1 code rather than
the size in Kb. Please see RM0038 r8 or newer for an explanation, as
noted in the comments.